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Fix udp15Server decrypt IV: use server_nonce, not client_nonce

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SetUDP15Crypto was initializing udp15Server with setup15(key,
serverNonce, clientNonce), which set decryptIV=clientNonce.
But the server encrypts with server_nonce, so the client-side
decryptIV must be server_nonce.

The incoming IV byte from the server was 0x58, but our decryptIV[0]
was 0xab (client_nonce[0]). Diff of -83, way outside the ±30
acceptance window.

Now udp15Server.decryptIV is directly set to server_nonce.
This commit is contained in:
Brandon McGinty (deepseek)
2026-08-09 02:30:28 -04:00
committed by Brandon McGinty
parent 4c7731043c
commit e93087afeb
1 changed files with 7 additions and 4 deletions
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gumble/gumble/udp15.go
+7 -4
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@@ -412,6 +412,8 @@ var udp15Client *cryptState15
var udp15Server *cryptState15 var udp15Server *cryptState15
// SetUDP15Crypto installs the 1.5 native UDP crypto state from CryptSetup. // SetUDP15Crypto installs the 1.5 native UDP crypto state from CryptSetup.
// udp15Client: encrypts with client_nonce (outbound).
// udp15Server: decrypts with server_nonce (inbound).
func SetUDP15Crypto(key, clientNonce, serverNonce []byte) { func SetUDP15Crypto(key, clientNonce, serverNonce []byte) {
csClient := &cryptState15{} csClient := &cryptState15{}
if err := csClient.setup15(key, clientNonce, serverNonce); err != nil { if err := csClient.setup15(key, clientNonce, serverNonce); err != nil {
@@ -420,11 +422,12 @@ func SetUDP15Crypto(key, clientNonce, serverNonce []byte) {
} }
udp15Client = csClient udp15Client = csClient
// Server state: we only use decryptIV (to decrypt server→client packets).
// The server encrypts with server_nonce, so our decryptIV must be server_nonce.
csServer := &cryptState15{} csServer := &cryptState15{}
if err := csServer.setup15(key, serverNonce, clientNonce); err != nil { copy(csServer.key[:], key)
log.Error("SetUDP15Crypto server: %v", err) copy(csServer.decryptIV[:], serverNonce)
return csServer.initialized = true
}
udp15Server = csServer udp15Server = csServer
log.Info("Mumble 1.5 native UDP crypto initialized") log.Info("Mumble 1.5 native UDP crypto initialized")